/Engine/Source/Runtime/GeometryCore/Public/DynamicMeshEditor.h
Find "new" UV for input UV element underIndexmapping, or create new if missing
index of duplicate UV in given UV layer
int FindOrCreateDuplicateUV ( int ElementID, int UVLayerIndex, [FMeshIndexMappings](API\Runtime\GeometryCore\DynamicMesh\FMeshIndexMappings) & IndexMaps )